Blending options effect is not immediately visible.

Hi!

I was busy with Photoshop CS5 this afternoon until suddenly the blending options did were not directly applied to the layer. The preview checkbox is checked but I still don't see any results. The strange thing is that when I uncheck the box the result does show. I probably hit a button but I don't know which one. Can someone tell me what the cause of this could be?

Thanks!

I know I shouldn't double post but I just found something else out.
The same thing happened again with another project. It seems that it occurs when I'm doing something with the Blending options. When I check an option in Blending options and then uncheck it for example color overlay Than in the layer menu color overlay will stay visible below effects and below the corresponding layer but without the eye. Although when I turn on the eye then still nothing happens. There is also an fx behind the layer. i hope this will give someone an idea. Thanks!